xDSL is a collective name of all DSL (Digital Subscriber Line, digital subscriber line) technologies, and a technology for transmitting high-speed data on a telephone twisted-pair cable. A manner of frequency division multiplexing is commonly adopted to simultaneously transmit an xDSL and a POTS (Plain Old Telephone Service, plain old telephone service) on a twisted-pair cable, where the xDSL occupies a high frequency band part, the POTS occupies a baseband part lower than 4 KHz, and signals on the two parts are divided by a divider. A system for providing multiple lines of xDSL access is called a DSLAM (DSL Access Multiplexer, DSL access multiplexer).
With the development of the xDSL technology, the xDSL technology utilizes an increasingly wider frequency band, and bears an increasingly higher speed. With an increase in a frequency band, crosstalk between twisted-pair cables has an increasingly larger impact, especially in the high frequency band part. Crosstalk is generally categorized as near-end crosstalk (NEXT) and far-end crosstalk (FEXT). Because uplink and downlink channels of an xDSL adopt frequency division multiplexing, an impact of the NEXT on a system may be ignored. However, the FEXT has a big impact on transmission performance of a line. Therefore, a method for effectively determining a source of crosstalk between lines and a crosstalk relationship between lines is needed.
The following method is proposed to determine a source of crosstalk between lines and crosstalk between lines. In the method, within a fixed time interval, transmission power of a line (referred to as a line 2 in the following) and a signal-to-noise ratio of another line (referred to as a line 1 in the following) are collected with each subcarrier as a unit; a variance of the transmission power of the line 2 is determined; noise on the line 1 is determined; a coefficient of crosstalk of the line 2 into the line 1 at a specific frequency point is determined, that is, the crosstalk of the line 2 into the line 1 at the specific frequency point is determined. However, the foregoing method has the following problems: When an environment where a line works is relatively steady, and a transmission power spectrum of the line is also relatively stable, a variance occurs rarely. Therefore, it may take a long time to make collected data meet conditions of validity, resulting in that a long time is taken for crosstalk analysis and determination, and even an effective result cannot be obtained through convergence.
To resolve the foregoing problem, an improved solution of the foregoing method is further proposed, and in the solution, a transmission power spectrum is actively changed. However, a problem of the solution lies in that when a crosstalk source of a line or a crosstalk relationship between a line and another line needs to be tested, operations, such as frequent changing of a configuration and deactivation on all lines, are needed, thereby seriously affecting a normal service.